1. Field of the Invention
The present invention relates generally to turbine air seal rings.
2. Description of the Prior Art
Turbine blades of a gas turbine have employed a multiplicity of blades mounted around the peripheral portion of a rotatable disk. The disk rotated within an enclosed duct of a gas turbine under the drive forces of gases which have a high pressure and a high temperature. Air seals are required between the ducts and the circumferential rings formed by mating shrouds of the turbine disc to seal the gases in the turbines. The knife edge components which form the turbine air seals are relatively thin, typically on the order of 0.018 to 0.020 inches thick, and are typically formed from nickel based super alloys.
High temperature gases which pass over the turbine air seals cause the turbine air seals to wear or corrode. The thermal effects of combustion gas contaminants, the thermal stresses imposed by the cyclic nature of the operation of the turbine and the frictional engagement of the rotating disc against the stationary turbine outer air seal are some of the factors which cause damage to the air seals over time. A principal manifestation of the damage is an increase in the clearance gap between the seals and the disc. The increase in the clearance gap decreases the turbine efficiencies due to the power loss from escaping gases. In addition, turbine components which are heated by the escaping hot gases tend to deteriorate. A significant segment of turbine technology is directed to the repair of turbine air seals and the maintenance of air seal integrity.
Recently, one of the major turbine vendors, Westinghouse, has begun providing an air seal ring which uses wire brushes for sealing purposes. The wire brush air seals are provided in air brush rings. The wire brush air seals mounted in such rings have been asserted to increase cooling and efficiency. However, existing knife edge seal rings were not adapted to receive the new wire brush modifications. If an existing air seal ring was modified to receive the new wire brush ring, too much material from the existing ring had to be removed. There was inadequate structural support for the brush ring. Therefore, the existing ring had to be scrapped and a new replacement air seal purchased. The new replacement air seal was specifically sized to receive the wire brush ring with adequate support. However, the new replacement air seal was costly, and scrapping the entire prior existing ring to install a new ring fitted with the wire brush was wasteful and inefficient.
Other conventional turbine air seal repair technology involved machining of portions of the corroded damaged knife edge portions and the application of a weld build-up of the worn seal edges. The weldment was then remachined to the original specifications of the turbine component. However, considerable design and tooling efforts were frequently expended in controlling the distortion inherent in the welding process which caused some weld metal shrinkage and part distortion. Additional tooling was frequently provided to correct distortion where shrinkage otherwise could not be controlled. The design and tooling requirements for controlling distortion could often result in a repair process which was not cost effective in comparison with the cost of new replacement parts.
U.S. Pat. Nos. 4,285,108; 4,028,788; 3,771,978 and 4,924,581 dealt with techniques for removal and replacement of damaged areas of conventional knife edge seals. Typically new knife edge seals were installed in place of the damaged ones. However, this did not provide the increased cooling and efficiency of the wire brush seals.
The present invention relates to turbine air seal replacement rings, such as those used in gas turbines in power generation, electrical power plants or other electrical energy production facilities. A method for repairing or updating turbine air seal rings is also provided. The replacement air seal rings of the present invention provide a first seal ring portion having an annular groove formed therein, a second seal ring portion having a wire brush seal formed thereon and a mounting ring fitted into the annular groove of the first seal ring portion and being capable of receiving the second seal ring portion therein. The first seal ring portion may also have a plurality of knife edge seals formed thereon. The present invention also provides an adapter for repairing or converting a turbine air seal for use with a replacement seal ring. The adapter has a mounting ring for connecting a replacement wire brush seal ring to a knife edge seal ring of a gas turbine.
The gas turbine seal ring of the present invention provides a first seal ring portion having an inner wall from which a plurality of knife edge seals extend inwardly. The seals may be of any suitable number and dimension, as determined by the specific application for which the seal ring is used. An annular groove, channel or seat is formed in the first seal ring portion, the channel being capable of receiving a mounting ring therein. Typically, the annular groove is formed by milling or cutting material from a first seal ring portion of an existing seal ring.
The mounting ring provides an increased inner diameter to the air seal ring, thereby allowing installation of the new or improved second seal ring portion. The mounting ring is formed having an outer diameter or surface substantially conforming to the inner diameter or surface of the annular groove formed in the first seal ring portion. The mounting ring further has a generally rectangular cross sectional shape and may have at least one knife edge seal formed on an inner surface and extending inwardly therefrom. A cylindrical slot or seat is formed in the mounting ring, outwardly from the inner surface thereof. The slot partially defines an inner lip or edge of sufficient thickness to support and retain the second seal ring portion.
The second seal ring portion is securely fitted or mounted in the cylindrical channel formed in the mounting ring. A wire brush seal extends inwardly from the inner surface of the second seal ring portion, the wire brush seal being comprised of a plurality of relatively small bristle elements.
The adapter of the present invention provides a mounting ring for fitting into an annular groove in a knife edge seal ring and a replacement seal ring having a wire brush seal extending inwardly from an inner surface thereof. Depending on the specific application in which the adapter will be used, the mounting ring may have at least one or a plurality of knife edge seals extending inwardly from an inner surface. A cylindrical lip portion may be provided in the mounting ring for providing a support rim or shoulder for supporting and retaining the replacement seal ring, the lip extending between an inner surface and an annular slot or seat of the mounting ring.
The method of the present invention provides for first cutting or milling an annular groove or channel in the interior surface of the air seal ring. The milling process involves removing only a relatively small portion of material from the seal ring, sufficient to allow attachment of the mounting ring. The mounting ring is then fitted or installed into the groove and further then secured or attached to the air seal ring, thereby creating a modified or improved air seal ring.